In order to improve the performance of voltage regulators whenever practical, the internal bias circuitry for the reference voltage and error or difference amplifier is directly derived from the regulated output voltage. As a result, these elements may not be self-starting when power is first applied to the regulator or when the output of the voltage regulator is shorted to ground. It is therefore required, in all these cases, to include start-up circuits to initiate and, if necessary, to maintain the flow of current independent of output conditions. Furthermore, most monolithic voltage regulators, in addition to current limit protection, also incorporate current foldback protection to prevent unnecessary power dissipation under short-circuit or current overload condition. This technique reduces the short-circuit current while still allowing full output current to be obtained during normal regulator operation.
Typically, current limit, current foldback protection, and start-up functions are distinct parts of the monolithic design and add to the complexity of the circuit.
In view of the foregoing, it is desirable to provide a current limiting circuit for a voltage regulator having the internal bias directly derived from the regulated output voltage, with current foldback protection provided directly using the start-up circuitry which initiates and maintains the flow of current independently of output condition.